Reed valve with multiple ports

ABSTRACT

A reed valve seat with multiple ports allows a reed valve to operate under extreme pressures in a variable cam timing system. A check valve includes a valve seat in a variable cam timing phaser with a contact surface and multiple ports for fluid in control passages within the phaser to flow through. A reed creates a seal with the contact surface of the valve seat when the reed contacts the valve seat such that reverse flow of fluid in the variable cam timing phaser is prevented.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention pertains to the field of valves for a variable cam timingsystem. More particularly, the invention pertains to a VCT with a reedvalve with multiple ports.

2. Description of Related Art

Engine performance of an engine having one or more camshafts can beimproved, specifically in terms of idle quality, fuel economy, reducedemissions, or increased torque, by way of a variable cam timing (VCT)system. Variable cam timing refers to controlling/varying the angularrelationship or phase between one or more camshafts, which drive theengine's intake and/or exhaust valves, and the crankshaft, which isconnected to the pistons. For example, the camshaft can be “retarded”for delayed closing of intake valves at idle for stability purposes andat high engine speed for enhanced output.

Likewise, the camshaft can be “advanced” for premature closing of intakevalves during mid-range operation to achieve higher volumetricefficiency with correspondingly higher levels of torque. In adual-camshaft engine, retarding or advancing the camshaft isaccomplished by changing the positional relationship of one of thecamshafts, usually the camshaft that operates the intake valves of theengine, relative to the other camshaft and the crankshaft. Accordingly,retarding or advancing the camshaft varies the timing of the engine interms of the operation of the intake valves relative to the exhaustvalves, or in terms of the operation of the valves relative to theposition of the crankshaft.

Many VCT systems incorporating hydraulics include an oscillatable rotorsecured to a camshaft within an enclosed housing, where a chamber isdefined between the rotor and housing. A “phaser” is all of the parts ofthe engine which allow the camshaft to run independently of thecrankshaft. In a vane phaser, the rotor includes vanes mounted outwardlytherefrom to divide the chamber into separated first and second fluidchambers. Such a VCT system often includes a fluid supplyingconfiguration to transfer fluid within the housing from one side of avane to the other, or vice versa, to thereby rotate the vane of therotor with respect to the housing in one direction or the other. Suchrotation is effective to advance or retard the position of the camshaftrelative to the crankshaft. These VCT systems may either be“self-powered” having a hydraulic system actuated in response to torquepulses flowing through the camshaft, or may be powered directly from oilpressure from an oil pump. Additionally, mechanical connecting devicesare included to lock the rotor and housing in either a fully advanced orfully retarded position relative to one another. Check valves are usedto control the oil flow to the fluid chambers in the vanes. Check valvesallow oil to flow freely in one direction while preventing the oil fromgoing in the opposite direction.

In a conventional VCT system, prior art reed check valves cover a singleport with support only at the edges of the diameter. The single portdesign creates difficulties because of the physical limits of thematerial properties for the reed valve. When the check valve is“closed”, the reed valve is sealed across the seat, and preventsbackflow (zero backflow). In this position, the backpressure on the reedvalve may be high enough to plastically deform and eventually cause thereed valve to fail.

Referring to FIGS. 1 and 2, a prior art reed valve assembly (4) isshown. A reed valve (5) covers the reed valve seat (1). There is asingle port (2), or hole, in the reed valve seat (1). The system exertsbackpressure (3) on the reed (5), which may eventually cause the reedvalve to fail.

To reduce the stress on the valve and eliminate the chance of failure,the seat diameter (hole/port size) may be reduced. But, reducing theseat diameter restricts flow, and negatively affects VCT performance.

Therefore, there is a need in the art for an improved design for a reedvalve that can sustain high pressures without restricting flow.

SUMMARY OF THE INVENTION

A reed valve seat with multiple ports allows a reed valve to operateunder extreme pressures in a variable cam timing system. A check valveincludes a valve seat in a variable cam timing phaser with a contactsurface and multiple ports for fluid in control passages within thephaser to flow through. A reed creates a seal with the contact surfaceof the valve seat when the reed contacts the valve seat such thatreverse flow of fluid in the variable cam timing phaser is prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a top view of a prior art reed check valve seat with thereed valve removed.

FIG. 2 shows a cross-sectional view of a prior art reed check valve.

FIG. 3 shows a top view of a reed check valve seat with the reed valveremoved in an embodiment of the present invention.

FIG. 4 shows a cross-sectional view of a reed check valve in anembodiment of the present invention.

FIG. 5 shows a cam torque actuated (CTA) VCT mechanism in the nullposition in an embodiment of the present invention.

FIG. 6 shows a cam torque actuated VCT mechanism moving towards theretard position in an embodiment of the present invention.

FIG. 7 shows a cam torque actuated VCT mechanism moving towards theadvance position in an embodiment of the present invention.

FIG. 8 shows a rotary actuator in an embodiment of the presentinvention.

FIG. 9 shows a linear actuator in an embodiment of the presentinvention.

FIG. 10A shows a schematic of a phaser of the present invention with thespool valve in the null position.

FIG. 10B shows a schematic of the phaser of FIG. 10A moving towards theretard position.

FIG. 10C shows a schematic of the phaser of FIG. 10A moving towards theadvance position.

FIG. 11 shows a torsion assisted (TA) VCT mechanism with a single checkvalve in the null position in another embodiment of the presentinvention.

FIG. 12 shows a torsion assisted VCT mechanism with two check valves inthe null position in another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention improves a check valve seat design for a reedvalve. This reduces stress levels while maintaining or exceeding theflow rates of the single-holed valve seats of the prior art. By changingthe seat geometry from a single port to multiple smaller ports, theexposed surface area of each port is reduced. By decreasing the amountof exposed surface area, the stress on the reed is decreased. Thisdecreases the stress on the reed valve. By adding additional ports, thestress on the reed stays at acceptable levels, while the flow rate maybe increased. The flow rate depends on the entire area of the ports.Therefore, if the total area of the multiple ports is greater than thesingle port in the prior art, the flow rate is increased.

FIGS. 3 and 4 show a reed valve assembly (104) of the present invention.A reed (105) covers the reed valve seat (100). The reed valve seat (100)includes multiple ports, or holes (102). Although the system exertsbackpressure (103) on the reed (105), the exposed surface area below thereed (105) for each port (102) is reduced because of the smaller ports(102). This decreases the effect the backpressure (103) has on thesystem. Consequently, the stress on the reed (105) does not deform thereed, while the flow rate in the reed valve (104) may be increased overthe prior art reed valve (4). The reed valve assembly (104) describedwith reference to FIGS. 3 and 4, is also represented by reed valveassembly (204) in subsequent figures.

Although four ports, all with the same diameter and area, are shown inthe Figure, the present invention is not limited to four ports or portsthat are all the same size. The number of ports and their desired sizeis system dependent. It depends on the rate at which the phaser is goingto be moved and on the total torsional energy available. Packaging alsoaffects the number of ports used.

For example, since the pressure and energy are known for a given system,the preferred port area is the largest port area that can withstand thepressure in that system. To obtain the same amount of flow in the reedvalves of the present invention as with the single holed reed valves ofthe prior art, one would use a number of ports with an area that wouldtogether be equal or greater than the same area of the single port.Alternatively, the ports may have different areas as long as the totalarea is equal or greater than the area of the single port. If less orgreater flow rates are desired than that obtained with a single port,the ports and their areas are adjusted accordingly.

Assume, for example, that a 6 mm diameter single port provides a certaindesired flow rate in a particular system. Assume also that a 3 mm portis the largest size port able to withstand the pressure in that system.Flow is controlled by the area available. A 6 mm hole has an area of28.27 mm², while a 3 mm hole has an area of 7.07 mm². 28.27 mm² dividedby 7.07 mm² equals 4. Thus, four ports, each with a 3 mm diameter,result in the same area as the 6 mm single port of the prior art. A reedvalve assembly with four 3 mm ports is able to withstand higherpressures than a single 6 mm port, while maintaining the same area.

Alternatively, multiple ports may have an increased area compared to asingle port design. A valve with a 5.5 mm diameter single port providesa certain desired flow rate in a particular system. This single port hasan area of 23.75 mm². A valve with four ports, each having a diameter of3.5 mm and an area of 9.62 mm , has a total area of 38.48 mm².

FIGS. 5 through 7 show one example of a VCT system using the reed valve(104) of the present invention. In these figures, reed valves (104) and(204) with multiple ports replace reed valves and other check valves asknown in the prior art.

In a cam torque actuated (CTA) phaser, torque reversals in the camshaftcaused by the forces of opening and closing the valves move the vane(76). The CTA advance and retard chambers (78), (80) are arranged toresist positive and negative torque pulses in the camshaft and arealternatively pressurized by the cam torque. The control valve, shown asa spool valve (74) in the figures, includes a spool (79) and is receivedin a sleeve (87) of the rotor. The position of the spool (79) controlsthe motion (e.g. to move towards the advance position or the retardposition) of the phaser. The spool valve (74) in the CTA system allowsthe rotor in the phaser to move by permitting fluid flow from theadvance chamber (78) to the retard chamber (80) or vice versa, dependingon the desired direction of movement. Positive cam torsionals are usedto retard the phaser and negative cam torsionals are used to advance thephaser.

More specifically, in the null position, as shown in FIG. 5, the spoolis positioned such that spool lands (79 a), (79 b) block lines (82) and(83), and vane (76) is locked into position. An inlet flow check valve(89) maintains system pressure by allowing additional fluid to thephaser from an external source through a supply line (88) to make up forlosses due to leakage only. Although the inlet flow check valve (89) isshown as a ball check valve in the figures, the reed valve of thepresent invention could alternatively be used as the inlet flow checkvalve (89) in the supply line (88). An inlet flow reed check valve (89)may need less flow than the check valves (104) and (204), and thereforemay require less and/or smaller ports than the ports for check valves(104) and (204).

FIG. 6 shows the phaser moving towards the retard position. The spool ispositioned such that spool land (79 b) blocks line (83) and lines (82)and (86) are open. Fluid exits the advance chamber (78) through line(82) and moves through the spool between the lands and back into line(86), where it feeds into line (83) supplying fluid to the retardchamber (80). Positive cam torsionals are used to help move the vane(76).

Makeup oil is supplied to the phaser to make up for leakage and entersline (88) through the check valve (89), and moves into the necessarychamber.

FIG. 7 shows the phaser moving towards the advance position. The spoolis positioned so that the spool land (79 a) blocks line (82) and lines(83) and (86) are open. Fluid exits the retard chamber (80) through line(83) and fluid moves through the spool between the lands and back intoline (86) where it feeds into line (82) supplying fluid to the advancechamber (78). Negative cam torsionals are used to move the vane (76).

Makeup oil is supplied to the phaser to make up for leakage and entersline (88) through the check valve (89), and moves into the necessarychamber.

In another embodiment, the spool valve (74) may also be externally orinternally connected to a stationary rotary actuator. The housing in arotary actuator does not have an outer circumference for accepting driveforce and motion of the housing is restricted as shown by the two-headedarrow (250). The restriction of the housing ranges from not moving thehousing at all to the housing having motion restricted to less than360°. All movement, other than the twisting of the shaft is done by therotor. The rotor and the vane move or swing through the distance asdefined and limited by the housing. All of the cyclic load is on therotor and the rotor accepts all of the drive force.

FIG. 8 shows a CTA-like rotary actuator, which operates similar to theCTA phaser discussed above, in this embodiment of the present invention.The rotary actuator is operated by reciprocating torque. Circulatinghydraulic fluid is used with check valves in the rotary actuator. Thissystem uses torque actuating technology without a camshaft. The shaft(203) is moved relative to a fixed point.

In this embodiment, the spool valve (74) may by externally or internallyconnected to the stationary rotary actuator (200). In the rotaryactuator (200), the housing (201) does not have an outer circumferencefor accepting drive force and motion of the housing is restricted. Astop (202) restricts (250) the movement of the rotary actuator to lessthan 360°. The rotary actuator includes reed valves (104) and (204) withmultiple ports to withstand high pressure.

In another embodiment, shown in FIG. 9, the reed valves (104) and (204)are used with a spool valve (74) externally or internally connected to alinear actuator (500). A linear actuator typically includes a housing(501) and a piston (502). The piston (502) moves within the housing(501) in response to fluid pressure. Seals (503) are also included inthe actuator (500). The reed valves (104) and (204) have multiple portsto withstand high pressure.

In another embodiment, the CTA system described above is preferablymounted to the side of the engine in a self contained unit. In thisembodiment, the CTA system, including the reed check valves (104) and(204) of the present invention, as well as the spool valve, is packagedin the self-contained unit mounted to the side of the engine.

In the cam torque actuated (CTA) phaser shown in FIGS. 10A through 10C,torque reversals in the camshaft caused by the forces of opening andclosing the valves move the rotor (406). The CTA advance and retardchambers (402), (404) are arranged to resist positive and negativetorque pulses in the camshaft and are alternatively pressurized by thecam torque. The control valve, which usually includes a spool valve(409) with a spool (428), is received in a sleeve (422) of the rotor.The position of the spool (428) controls the motion (e.g. to movetowards the advance position or the retard position) of the phaser. Thespool valve (428) in the CTA system allows the rotor (406) in the phaserto move by permitting fluid flow from the advance chamber (402) to theretard chamber (404) or vice versa, depending on the desired directionof movement. Positive cam torsionals are used to retard the phaser andnegative cam torsionals are used to advance the phaser. During operationof the CTA phaser, cam torques pressurize both the advance (402) andretard chambers (404) simultaneously and oil circulates to and from thespool valve (428) to the chambers (402) and (404).

FIG. 10A shows a schematic of the phaser in this embodiment with thespool valve in the null position. An inlet flow check valve (424)maintains system pressure by allowing additional fluid from an externalsource through a supply line (418) to the remotely or separately locatedcontrol system from the rotor and housing, indicated in the figure bydashed box (430), to make up for losses due to leakage only. The controlsystem (430) includes the spool valve (409), the actuator (403), commonline (416), reed check valves (104) and (204) and portions of advanceline (408) and retard line (410). The spool valve (409) includes a spool(428) with multiple lands (428 a), (428 b) slidably received by a bore(422). One side of the spool (428) is biased by spring (420) and theother side of the spool (404) is biased by the actuator (403). Advanceand retard lines (408) and (410) lead from the remotely mounted controlsystem (430), through the camshaft (426) to the advance chamber (402)and the retard chamber (404) located in the housing (405).

In terms of the spool valve, the force of the actuator and the force ofthe spring are balanced in the null position and the spool is positionedsuch that fluid from the supply enters the spool valve (428) and movesthrough common line (416) and reed check valves (104), (204) to theadvance line (408) and the retard line (410) respectively. From theadvance line (408) and the retard line (410) fluid enters the advancechamber (402) and the retard chamber (404).

To move towards the retard position, as shown in FIG. 10B, the force ofthe actuator (403) was increased and the spool valve moved to the leftby the actuator until the spring force balanced the force of theactuator. Because the spool (428) has changed position, positive camtorque energy causes the vane (406) to move in the retard direction.Fluid is able to exit the advance chamber (402) through advance line(408) and the camshaft (426) to the remote control system (430) and intothe spool valve (409). Fluid from the spool valve (428) enters commonline (416) and moves through reed check valve (204) to retard line (410)and to the retard chamber (404). Spool land (428b) blocks fluid from theretard chamber (404) from entering the spool valve (409). Reed checkvalve (204) does not allow fluid to exit from the retard chamber (404).

Makeup oil is supplied to the phaser to make up for leakage and entersline (418) through the check valve (424), and moves into the necessarychamber.

To move towards the advance position, as shown in FIG. 10C, the force ofthe actuator (403) was decreased and the spool valve moved to the rightby the spring until the spring force balanced the force of the actuator.Because the spool (428) has changed position positive cam torque energycauses the vane (406) to move in the advance direction. Fluid is able toexit the retard chamber (404) through retard line (410) and the camshaft(426) to the remote control system (430) and into the spool valve (409).Fluid from the spool valve (428) enters common line (416) and movesthrough reed check valve (104) to advance line (408) and to the advancechamber (402). Spool land (428 a) blocks fluid from the advance chamber(402) from entering the spool valve (409). Reed check valve (104) doesnot allow fluid to exit from the advance chamber (402).

Makeup oil is supplied to the phaser to make up for leakage and entersline (418) through the check valve (424), and moves into the necessarychamber.

As in other embodiments, although check valve (424) is shown as a ballcheck valve in the figures, the check valve (424) may be a reed checkvalve (104) of the present invention.

In yet another embodiment, the reed valve (104) of the present inventionis used in a torsion assist (TA) VCT system. U.S. Pat. No. 6,883,481,issued Apr. 26, 2005, entitled “Torsional Assisted Multi-Position CamIndexer Having Controls Located in Rotor” discloses a single check valveTA, and is herein incorporated by reference. FIG. 11 shows a singlevalve torsion assist system in the null position.

The phaser operating fluid, illustratively in the form of enginelubricating oil, flows into the recesses (302) (labeled “A” for“advance”) and (303) (labeled “R” for “retard”) by way of a common inletline (313). An inlet reed check valve (104) prevents the hydraulic fluidfrom backflowing into the engine oil supply. Compared to the checkvalves (104) and (204) in FIGS. 5 through 7, the reed check valve (104)in the TA system would preferably require more and/or larger diameterports, to replenish the fluid supply, since fluid is exhausted out inthis system.

Inlet line (313) terminates as it enters the spool valve (320). Thespool valve (320) includes a spool (322). The spool (322), which ispreferably a vented spool, is slidable back and forth. The spool (322)includes spool lands (319) and (320). The spool lands (319) and (320)are preferably cylindrical lands and the spool preferably has threepositions. The null position is shown in FIG. 10. Control of theposition of spool (322) is in direct response to an actuator (321). Inone embodiment, the actuator is a variable force solenoid.

To maintain a phase angle, the spool (322) is positioned at null. Thecamshaft is maintained in a selected intermediate position relative tothe crankshaft of the associated engine, referred to as the “null”position of the spool (322). Make up oil from the supply fills bothchambers (302) and (303). When the spool (322) is in the null position,spool lands (319) and (320) block both of the inlet lines (308) and(310).

FIG. 12 shows a two check valve TA system. U.S. Pat. No. 6,763,791,issued Jul. 20, 2004, entitled “Cam Phaser for Engines Having Two CheckValves in Rotor Between Chambers and Spool Valve” discloses two checkvalve TA, and is herein incorporated by reference. In this embodiment,like reference numerals describe the same elements as described withrespect to FIG. 10.

Advance chamber reed check valve (104) is located in the advance chamberinlet line (308) while retard chamber reed check valve (204) is locatedin the retard chamber inlet line (310). Having the check valves in theadvance and retard chambers instead of having a single check valve inthe supply reduces leakage.

Accordingly, it is to be understood that the embodiments of theinvention herein described are merely illustrative of the application ofthe principles of the invention. Reference herein to details of theillustrated embodiments is not intended to limit the scope of theclaims, which themselves recite those features regarded as essential tothe invention.

1. A check valve comprising: a) a valve seat in a variable cam timingphaser comprising a contact surface and having a plurality of ports forfluid in control passages within the phaser to flow through; and b) areed that creates a seal with the contact surface of the valve seat whenthe reed contacts the valve seat; such that reverse flow of fluid in thevariable cam timing phaser is prevented.
 2. A variable cam timing phasercomprising: a) a housing having an outer circumference for acceptingdrive force; b) a rotor for connection to a camshaft coaxially locatedwithin the housing, the housing and the rotor defining at least one vaneseparating a plurality of chambers, at least one chamber being anadvance chamber and another chamber being a retard chamber, the vanebeing capable of rotation to shift the relative angular position of thehousing and the rotor; c) a spool valve comprising a spool having aplurality of lands slidably mounted within a bore in the rotor, thespool slidable from an advance position through a null position to aretard position; d) a plurality of control passages in the housing andthe rotor for selectively permitting fluid flow from the spool valve tothe advance chamber and the retard chamber, wherein the lands of thespool block and connect the control passages such that by slidablymoving the spool, the flow of fluid from a fluid input to the advancechamber and the retard chamber is controlled, varying the rotationalmovement of the housing relative to the rotor; and e) at least one checkvalve comprising a valve seat comprising a contact surface and having aplurality of ports for fluid in the control passages to flow through,and a reed that creates a seal with the contact surface of the valveseat when the reed contacts the valve seat, such that reverse flow offluid through the check valve is prevented.
 3. The variable cam timingphaser of claim 2, wherein the spool comprises length and a first landand a second land, spaced apart a distance along the length, such thatthe first land and the second land have a circumference which provides afluid blocking fit in a cylindrical recess of the rotor, and the lengthhas a lesser circumference than the first land and the second land topermit fluid to flow; and the cylindrical recess of the rotorcomprising, in spaced-apart relationship along a length of thecylindrical recess from a first end of the cylindrical recess mostdistant from the camshaft to a second end of the cylindrical recessclosest to the camshaft: a first exhaust vent connecting the cylindricalrecess to atmosphere; a first return passage connecting the advancechamber to the cylindrical recess; a first movement passage connectingthe cylindrical recess to the advance chamber; a central inlet passageconnecting a central location in the cylindrical recess to a source offluid; a second movement passage connecting the cylindrical recess tothe retard chamber; a second return passage connecting the retardchamber to the cylindrical recess; a second exhaust vent connecting thecylindrical recess to atmosphere; the first exhaust vent, second exhaustvent, first return passage, second return passage, first movementpassage, second movement passage and central inlet passage being spacedapart along the length of the cylindrical recess, and the first land andthe second land being of sufficient length and distance apart such that;when the spool is in a central position between the first end of thecentral recess and the second end of the central recess, the first landblocks the first return passage and the first movement passage, and thesecond land blocks the second movement passage and the second returnpassage; when the spool is in a position nearer the first end of thecentral recess, the first movement passage and second return passage areunblocked, fluid from the central inlet passage flows into the firstmovement passage and the advance chamber, and fluid from the retardchamber flows into the second return passage and the second exhaustvent; and when the spool is in a position nearer the second and of thecentral recess, the second movement passage and first return passage areunblocked, fluid from the central inlet passage flows into the secondmovement passage and the retard chamber, and fluid from the advancechamber flows into the first return passage and the first exhaust vent.4. The variable cam timing phaser of claim 2, wherein the check valvecomprises a first check valve and a second check valve; wherein therotor further comprises a central cylindrical recess located along anaxis of rotation; wherein the central cylindrical recess of the rotorcomprises: a first movement passage connecting the cylindrical recess tothe advance chamber, wherein the first check valve is located within thefirst movement passage, such that the first check valve is positioned topermit flow of fluid into the advance chamber; a second movement passageconnecting the cylindrical recess to the retard chamber, wherein thesecond check valve located within the second movement passage, such thatthe second check valve is positioned to permit flow of fluid into theretard chamber.
 5. The variable cam timing phaser of claim 2; whereinthe check valve comprises a first check valve and a second check valvein the plurality of control passages connecting the advance chamber andthe retard chamber, wherein the plurality of control passagesrecirculate fluid to and from the spool valve to the advance chamber andthe retard chamber.
 6. The variable cam timing phaser of claim 2,wherein the variable cam timing phaser is selected from the groupconsisting of a cam torque actuated phaser and a torsion-assist phaser.7. A check valve comprising: a) a valve seat in a rotary actuatorcomprising a contact surface and having a plurality of ports for fluidin control passages within the rotary actuator to flow through; and b) areed that creates a seal with the contact surface of the valve seat whenthe reed contacts the valve seat; such that reverse flow of fluid in therotary actuator is prevented.
 8. A rotary actuator comprising at leastone camshaft comprising: a fixed part with motion restricted to lessthan 360°, and a rotating part for accepting drive force and connectionto a shaft coaxially located within the fixed part, the fixed part andthe rotating part defining at least one vane separating a chamber in thefixed part into a clockwise chamber and a counterclockwise chamber, thevane being capable of rotation to shift the relative angular position ofthe fixed part and the rotating part; and a check valve comprising avalve seat comprising a contact surface and having a plurality of portsfor fluid in control passages within the rotary actuator to flowthrough, and a reed that creates a seal with the contact surface of thevalve seat when the reed contacts the Valve seat, such that reverse flowof fluid in the rotary actuator is prevented.
 9. A check valvecomprising: a) a valve seat in a linear actuator comprising a contactsurface and having a plurality of ports for fluid in control passageswithin the linear actuator to flow through; and b) a reed that creates aseal with the contact surface of the valve seat when the reed contactsthe valve seat; such that reverse flow of fluid in the linear actuatoris prevented.
 10. A linear actuator, comprising: a housing; a pistonthat moves within the housing in response to fluid pressure; and a checkvalve comprising a valve seat comprising a contact surface and having aplurality of ports for fluid in control passages within the linearactuator to flow through, and a reed that creates a seal with thecontact surface of the valve seat when the reed contacts the valve seat,such that reverse flow of fluid in the linear actuator is prevented.